The present disclosure relates to a power semiconductor device having enhanced reliability.
An insulated-gate bipolar transistor (IGBT) is a transistor with a gate manufactured by using a metal-oxide semiconductor (MOS) structure and forming a p-type collector layer on a rear surface thereof having bipolarity.
Since the development of conventional power Metal-Oxide Semiconductor Field Emission Transistors (MOSFET), such MOSFETs have been used in fields in which fast switching characteristics are required.
However, due to inherent structural limitations of MOSFETs, bipolar transistors, thyristors, gate turn-off thyristors (GTO), and the like, have been used in fields in which high voltage are required.
IGBTs, featuring low forward loss and fast switching speeds, tend to extendedly applied to applications in various fields for which existing thyristors, bipolar transistors, MOSFETs, and the like are unsuitable.
As for an operating principle of an IGBT, in the case that an IGBT device is turned on and a voltage higher than that of a cathode is applied to an anode, while a voltage higher than a threshold value of the device is applied to a gate electrode, a polarity of a surface of a p-type body region positioned in a lower end portion of the gate electrode is reversed to form an n-type channel.
An electron current injected into a drift region through the n-type channel induces injection of a hole current from a p-type collector layer having a high concentration positioned in a lower portion of the IGBT device, such as a base current of a bipolar transistor.
The injection of the minority carrier having a high concentration, increases conductivity in the drift region by tens to hundreds of times (an order of magnitude of one or two), causing conductivity modulation.
Unlike a MOSFET, a resistance component in the drift region may be reduced in size to be significantly low due to the conductivity modulation, and thus, extremely high voltages may be applied to IGBT devices.
A current flowing to a cathode may be divided into an electron current, flowing through a channel, and a hole current, flowing through a junction between a p-type body and an n-type drift region.
An IGBT may have a PNP structure between an anode and a cathode in terms of a substrate structure, so unlike a MOSFET, a diode may not be installed, and thus, a separate diode may need to be connected to an IGBT through an inverse-parallel connection.
Major characteristics of IGBTs include maintaining a blocking voltage, reducing conduction loss, and increasing a switching speed.
As for a structure of an IGBT, an IGBT includes an n+-type emitter region, a p-type body region an n− drift region, and a p+-type collector region, and thus, a PNPN parasitic thyristor structure exists.
Once the parasitic thyristor operates, the IGBT may not be subjected to being controlled by a gate any longer and a large amount of current may flow to an anode and a cathode to generate a high level of heat to burn the device.
The phenomenon in which a parasitic thyristor is increased is called latch-up.
Latch-up drastically lowers reliability of a device, and thus, a scheme for preventing latch-up is required.